Bones

Question 1

What are the components of the skeletal system?

Answer 1

There are 206 bones and 360 joints and adjacent cartilages. There are 126 appendicular bones.

Question 2

What are the functions of the skeletal system?

Answer 2

• Support – soft tissues
• Protection
• Movement – lever systems
• Blood cell production – red bone
  marrow (hematopoiesis)
• Mineral storage/release (calcium and
  phosphorus)
• Energy storage – yellow Marrow

Question 3

What are the classifications of bones?

Answer 3

• Long bones
• Short bones
• Irregular bones
• Flat bones

Question 4

What are the properties of bones?

Answer 4

Bones are anisotropic. The behaviour of the bone varies with the direction of the load application. Long bones can handle the greatest loads in the longitudinal direction and the least across the surface of the bone.

Question 5

What are the mechanical properties of bones?

Answer 5

Bone strength, stiffness, and energy depends on both the material composition and the structural properties of the bone. Mechanical properties also vary with age and gender.

Question 6

What forces do bones need to be capable of withstanding?

Answer 6

Static and dynamic forces. Bone must be capable of withstanding a variety of imposed forces simultaneously. Statically, bone resists the force of gravity, supports the weight of the body, and absorbs muscular activity produced to maintain the static posture. Dynamically e.g., running, the forces are magnified many times and become multidirectional.

Question 7

What is the composition of osseous tissue?

Answer 7

Most of the mass of the bone is formed by the bone matrix. The matrix consists of 50% organic material, (osteoblasts) made up of collagen and water/cells, and 50% inorganic material made up of calcium hydroxyapatite (calcium, phosphate and hydroxide).

Question 8

What is the purpose of collagen fibres in the matrix of osseous tissue?

Answer 8

They give the bone tensile strength.

Question 9

What is the purpose hypoxyapatite in the matrix of osseous tissue?

Answer 9

It causes compression of the osseous tissue.

Question 10

What are the 2 types of bones in bone histology?

Answer 10

Compact (cortical) bone, 80%, and cancellous (spongy) bone, 20%.

Question 11

What is the structure of compact (cortical) bones?

Answer 11

• Low porosity <15% (ratio of pore space to the total volume)
• High density
• High Mineralisation
• Little deformation withstands high levels of weight bearing and muscle tension in the longitudinal direction.

Question 12

What is the structure of cancellous (spongy) bone?

Answer 12

• High porosity
• Low density
• Greater deformational characteristics

Question 13

How is bone replaced?

Answer 13

It is replaced in a coupled process between bone deposition (by osteoblasts) and bone destruction/reabsorption (by osteoclasts).

Question 14

How often is bone replaced?

Answer 14

Spongy bone is replaced every 3-4 years and compact bone is replaced every 10 years.

Question 15

Why is bone replaced?

Answer 15

It prevents mineral salts from crystallizing, protecting against brittle bones and fractures.